Conventional water heating systems of the type used in most residences include relatively large holding tanks that contain enough water to supply a predetermined volume of heated water for a given period of time. The water is slowly heated to the desired temperature and then maintained at that temperature until needed. These conventional water heating systems typically require a significant amount of space and waste energy by maintaining the water at an elevated temperature for an extended period of time.
In response to these problems, a number of on-demand heaters have been developed. A major concern in the design of these heaters has been the inadequate flow rates through the system. One solution has generally involved the use of multiple heating chambers. A typical example is found in U.S. Pat. No. 4,567,350 which issued to Todd, Jr.
A second major concern is the most efficient method for controlling such a system. Most devices currently employ temperature control mechanisms. Some employ a mixture of temperature control mechanisms and pressure switch control devices as, for example, in the Todd, Jr. patent. The lack of sensitivity of these systems to pressure changes is still a major concern.
An additional problem with devices such as the device disclosed by Todd, Jr. is the necessity of replacing the entire unit if the volume and usage requirements change. Currently, the installation of a larger hot water heating unit may be necessary to accommodate increased usage requirements.